This invention relates generally to magnetic tape cassettes, and more particularly concerns improvements in tape positioning and tension control.
A number of problems exist in current cassette design. Among these are tape tension discontinuities which can arise during fast winding operation, and leading to tape pack slip, steps in winds and damage to the cassette during long term storage.
In addition, there are operating conditions under which a section of damaged tape can cause additional tape damage ultimately resulting in destruction of cassette operability. As an example, assume that a few layers of tape protrude above the otherwise level wound tape pancake. If this protruding tape section becomes damaged due to contact with the parallel housing walls, the damaged section will thereafter produce a rough wind acting to broaden the overall thickness (i.e. width) of the pancake. Once the opposite sides of the pancake respectively and simultaneously rub against the upper and lower interior walls of the cassette case, drag increases significantly and larger tensions are developed in the tape, enhancing the possibility of additional tape damage. The same problems can and do exist when thin, low friction liners are employed within the cassette case.
A further problem arises from insufficient tape tension. For example, consider the situation where, for a short period of time, the tape tension upstream and downstream of the "nip" between the capstan and pressure roller is zero. Since the axial alignment of the capstan and pressure roller cannot be perfectly parallel, the tape will tend to move upward, or downward along the face of the pressure roller during its lengthwise travel, and a number of opportunities then exist for subsequent tape damage. An additional problem is that of tape oscillation at the drive "nip", i.e. wandering of the tape on either side of center. Such oscillation can also lead to tape damage, i.e. such as buckling, ironing and wrinkling or creasing of the tape.
Summarizing, cassette failure is predominantly due to damage to, or improper guidance of, the tape within the case, in the course of the various modes of cassette operation. Known tape guidance devices, as for example those disclosed in U.S. Pat. Nos. 3,841,582 and 3,042,346, do not provide the unusual features of construction, mode of operation and results as are now afforded by the present invention.